The present invention relates to condensation resins obtained by the polycondensation of alkyl aryl ketones and formaldehyde and to a process for producing same in the liquid phase in the presence of basic catalysts at elevated temperatures.
Alkyl aryl ketone/formaldehyde resins have been known for a long time (DE-PS No. 892 975). According to that patent these resins are described as having softening points not exceeding about 80.degree. C. Even those stated values are attained only if alcohols of low molecular weight are introduced into the polycondensation mixture. On the other hand, the addition of alcohols involves the disadvantage that the proportion of alkyl aryl ketone built into the resin is clearly reduced. Moreover, more recent determinations of the softening points (melting point/capillary method) on the resins reproduced according to the state of the art have shown that the softening points actually attained are 5.degree. to 10.degree. C. below the stated maximum values.
More recently, a process was described for manufacturing ketone resins having improved softening points (EP-PS No. 7 106). However, this process is restricted to (cyclo) aliphatic ketone resins. The improvement is attained by the addition of phase transfer catalysts to the polycondensation mixture. It is typical for such catalysts that in practical use they must comprise a crown ether or a substituent having a very long alkyl chain which may where appropriate still have to comprise functional groups. The use of ketones comprising aromatic moieties is not described even though resins prepared therefrom have properties in their practical application which are at least as good. This peculiar fact can now be explained in light of our own tests, which have revealed that ketones comprising aromatic moieties, other synthesis conditions being the same, on addition of ammonium chloride as employed in the examples of EP-PS No. 7 106, will result in resins having low softening points.